This invention relates to an apparatus for detecting wear in a shaft or a bearing for a shaft in devices which utilize a rotating shaft positioned within a bearing. In one aspect of this invention, means are provided for detecting bearing or shaft wear in a sealed rotor pump.
A wide variety of devices utilize a rotating shaft positioned in a bearing such as motors, pumps or the like. In many instances, it is difficult to determine whether the bearing or shaft has worn to a degree where it must be taken out of service and replaced. Often times, continuing the use of a device having a worn bearing or shaft can lead to catastrophic results. For example, sealed rotor pumps often are utilized to pump corrosive and/or toxic liquids wherein the bearing and rotating shaft are immersed in the liquid. The shaft and bearing are out of view since they are sealed from the surrounding environment within the liquid. It is therefore difficult to determine whether undesirable wear has occurred
A wide variety of devices have been proposed to provide a warning of bearing or shaft wear. These devices generally are positioned remotely from the shaft or bearing to a position where the indication of undesirable wear can be readily perceived such as audibly or visibly. In U.S. Pat. No. 3,678,493 a device is disclosed for measuring shaft radial position in a bearing. Two probes are positioned so that they sense the shaft surface and produce a high frequency electrical signal proportional to the shaft position and motions. The device requires a static measurement utilizing a DC signal to obtain the initial displacement of the shaft from a bearing center and a dynamic measurement with an AC signal to obtain total displacement as the sum of initial displacement and shaft lip. The requirement of both an AC and DC signal requires a relatively complex means for signal processing. Accordingly, it would be desirable to provide a means which affords simple signal processing in order to determine bearing or shaft wear.
U.S. Pat. No. 3,981,621 discloses a bearing wear detection device which utilizes a single large coil surrounding a containment vessel for a rotating shaft. The coil is positioned coaxially with the rotating shaft which shaft has magnets mounted thereon. When the shaft is rotated, the magnets will not induce a voltage in the coil as long as the shaft remains at the center of the coil. When the shaft axis of rotation moves from the center, a voltage is induced in the coil. In this device, the placement of the coil is critical since any misalignment of the center of the coil and the axis of rotation will cause an induced voltage in the coil. In addition, the device does not have a capability of indicating the direction of bearing wear so that one cannot determine whether the wear is even about the axis of rotation or uneven. Thus, one cannot determine whether the bearing wear is trivial or whether the rotating shaft and bearing require replacement.
U.S. Pat. No. 3,373,300 discloses a means for detecting bearing or shaft wear by an electric alternate current generated by utilizing two coils positioned on a stator 180.degree. from each other. A voltage is induced in the coils when a rotor having rotor windings mounted thereon is rotated. The position of the shaft between the two stator winding then is determined by determining the difference in voltage induced in the two stator coils. The position of the stator coils must be precise since the device relies upon a predetermined air gap between the coils on the stator and the windings on the rotor. Furthermore, since only two stator coils are used, if there is a shift in shaft position which is equidistant from both stator coils, this shift will not be observed. Furthermore, since the induced voltage in the coils is dependent upon RPM of the shafts, the patented device must be operated at a constant RPM in order to render the induced voltages measured relevant to a shift in shaft position.
Additional examples of bearing wear detectors include U.S. Pat. Nos. 3,853,087; 3,614,731; 4,107,603; 4,199,718; 4,238,789; 4,423,635 and 4,584,865.
It would be desirable to provide a means for measuring bearing or shaft wear which is independent of shaft rotation, direction of shaft rotation, strength of magnets utilized in the detection device and independent of the size of a gap between the magnets and a sensor means.